1. Field of the Invention
The present invention relates to a mobile communication system which performs multicarrier communication by using a reference signal.
2. Description of the Related Art
As is generally known, adaptive modulation and coding (AMC) is a technique for improving a transmission rate and reception quality by executing modulation and coding in accordance with transmission path quality. Several arrangements have been proposed to implement AMC. The following arrangement is an example.
The receiving side measures wireless transmission path quality, and determines a transmission format (a combination of modulation and a coding ratio) which allows signal reception on the basis of the measured value. The receiving side then transmits the resultant data as a channel quality indication (CQI) to the transmitting side. The transmitting side selects a transmission format on the basis of the CQI and transmits transmission information on an information channel. This information is transmitted assuming that the type of transmission format of the information channel is a control channel.
That is, on the receiving side, the transmission format of an information channel can be known via the control channel, and the transmission information is received (see, for example, 3GPP TR 25.814 V1.0.1 (2005-11)). According to 3GPP TR 25.814 V1.0.1 (2005-11), the transmitting side is a base station, the receiving side is a terminal, the control channel is HS-SCCH, and the information channel is HS-PDSCH. HS-SCCH is transmitted before corresponding HS-PDSCH. The terminal receives HS-SCCH and obtains transmission format information necessary for the reception of HS-PDSCH. This system uses code division multiplexing (CDM), and hence multiplexes HS-SCCH and HS-PDSCH by changing codes.
In a multicarrier wireless communication system designed to form frames by division in the time direction and the frequency direction as in the orthogonal frequency division multiplexing (OFDM) scheme, it is difficult to insert a modulated information signal, a reference signal for synchronous detection, and a control signal representing the modulation coding information of the information signal at desired timings, respectively.
Conventionally, in order to accurately measure the wireless transmission path quality of each subcarrier on the receiving side, a reference signal is discretely inserted. A channel received before the reference signal is buffered, and transmission path estimation is performed by using the subsequently received reference signal. The buffered channel is then decoded on the basis of the estimation result. In addition, it is necessary to buffer a channel received during decoding. This Inevitably increases the buffer capacity.